In the literature of recent years conductive, colloidal nanocrystals have received much attention on account of their new optoelectronic, photovoltaic and catalytic properties. This makes them particularly interesting for future applications in the area of nanoelectronics, solar cells, sensors and biomedicine.
The development of conductive nanoparticles allows the use of new implementations and the envisioning of a multitude of new applications. Nanoparticles have a very significant surface/volume ratio and the substitution of their surface by surfactants brings about the changing of certain properties, in particular optical ones, and the possibility of dispersing them. Their small dimensions can bring about in certain instances effects of quantic confinement. The term nanoparticles is used when at least one of the dimensions of the particle is lower than or equal to 250 nm. The nanoparticles can be spheres (from 1 to 250 nm), small rods (L<200 to 300 nm), threads (several hundreds of nanometers or even several microns), disks, stars, pyramids, tetrapods, cubes or crystals when they do not have a predefined shape.
Several processes have been worked out in order to synthesize conductive nanoparticles. Among them, the following can be cited in a non-exhaustive manner:                physical processes:                    The deposition of chemical vapor (also known by the name “Chemical Vapor Deposition—CVD” when a substrate is exposed to volatilized chemical precursors which react or decompose on its surface. This process generally leads to the formation of nanoparticles whose morphology depends on the conditions used;            Thermal evaporation;            Epitaxy by molecular jets (also known by the name “Molecular Beam Epitaxy”) when atoms which will constitute the nanoparticles are bombarded at a high speed on the substrate (where they become fixed) in the form of a gaseous flux;                        chemical or physicochemical processes:                    Microemulsion;            Laser impulsion in solution when a solution containing a precursor is radiated by laser beam. The nanoparticles are formed in the solution along the luminous beam;            Synthesis by radiation with microwaves;            Oriented synthesis assisted by surfactants;            Synthesis under ultrasounds;            Electrochemical synthesis;            Organometallic synthesis;            Synthesis in an alcoholic environment.                        
The physical syntheses consume more raw materials with significant losses. They generally necessitate time and elevated temperatures, which makes them not very attractive for being used in a production on an industrial scale. This makes them not able to be adapted to certain substrates, for example, flexible substrates. Furthermore, the syntheses are carried out directly on the substrates in frames with reduced dimensions. These production modes prove to be relatively rigid and do not allow a production on substrates of large dimensions; however, they can be perfectly suited for the production of nanoparticles of silver used in formulations for ink according to the present invention.
As for the chemical syntheses, they have numerous advantages. The first one is the working in solution, wherein the conductive nanoparticles obtained in this manner are already dispersed in a solvent, which facilitates the storage and the use. In the majority of cases the nanoparticles are not fixed to a substrate at the end of the synthesis, which leads to greater latitude in their use. This opens the way to using substrates of different sizes and of different natures. These methods also allow a better control of the raw materials used and limits losses. A good adjustment of the synthesis parameters results in a good control of the synthesis and of the kinetics of the growth of the conductive nanoparticles. This allows a good reproducibility between the lots to be guaranteed as well as a good control of the final morphology of the nanoparticles. The ability to produce nanoparticles rapidly and in a great quantity with a chemical pathway while guaranteeing a certain flexibility to the product allows a production on an industrial scale to be envisioned. The obtention of dispersed, conductive nanoparticles opens numerous perspectives regarding their customization. Therefore, it is possible to adjust the nature of the stabilizers present on the surface of the nanoparticles according to the intended application. In fact, there are different methods of deposition using a moist pathway. In each case, particular attention must be given to the physical properties of the inks such as the surface tension or the viscosity. The adjuvants used during the formulation of the ink based on nanoparticles will allow adherence to the requirements of the deposition method. However, the surface ligands will also impact these parameters and their selection proves to be decisive. It is therefore important to have a view of the entirely of the ink in order to combine all the actors—nanoparticles, solvent, ligands and adjuvants—and to obtain a product compatible with the intended applications.